pterygium

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An abnormal mass of tissue arising from the conjunctiva of the inner corner of the eye that obstructs vision by growing over the cornea.

Century Dictionary and Cyclopedia

1. n. In zoology and anatomy, a limb or member of one of the vertebrates, as a fish, in the most general sense, without reference to its specialization in any given instance. A hypothetical pterygium, whence other pterygia are supposed to have been evolved, is an archipterygium; the ichthyic modification is an ichthyopterygium; the air-breathers' modification is a chiropterygium. Parts of the pterygium of an elasmobranchiate fish have been called mesopterygium, metapterygium, propterygium, bearing basalia and radialia, as in the accompanying figure.
2. n. In pathology, a more or less triangular patch of hypertrophied conjunctiva and subconjunctival tissue with its apex at the edge of the cornea or upon the cornea.
3. n. In entomology, one of the two lateral expansions at the end of the rostrum of certain weevils. They lie above and partly conceal the scrobes or grooves in which the antennæ are concealed.
4. n. An instrument employed in the operation for the removal of a pterygium from the cornea.
5. n. A forward growth of the eponychium over the nail-plate.

Wiktionary

1. n. medicine An abnormal mass of tissue in the corner of the eye that obstructs vision

GNU Webster's 1913

1. n. (Med.) A superficial growth of vascular tissue radiating in a fanlike manner from the cornea over the surface of the eye.

WordNet 3.0

1. n. either of two thickened triangular layers of conjunctiva extending from the nasal edge of the eye to the cornea; it arises from irritation of the pinguecula